🛡️Immunobiology Unit 11 – Immune Tolerance and Autoimmunity
Immune tolerance is the body's ability to recognize and not attack its own cells. This delicate balance prevents autoimmunity, where the immune system mistakenly targets self-antigens. Central and peripheral tolerance mechanisms work together to maintain this equilibrium.
When tolerance fails, autoimmune diseases can develop. These conditions range from organ-specific to systemic, impacting various body parts. Diagnosis involves detecting autoantibodies and assessing organ function. Treatment aims to suppress the immune response and manage symptoms.
Ignorance refers to the lack of interaction between self-reactive lymphocytes and their cognate antigens due to spatial separation or low antigen concentration
Apoptosis of self-reactive cells in the periphery is induced by the engagement of death receptors (Fas) or the withdrawal of survival factors
Types of Autoimmunity
Organ-specific autoimmunity targets specific organs or tissues, such as the pancreas in type 1 diabetes or the thyroid in Hashimoto's thyroiditis
Characterized by the presence of autoantibodies and T cells specific to organ-specific antigens
Systemic autoimmunity affects multiple organs and tissues throughout the body, as seen in systemic lupus erythematosus (SLE) and rheumatoid arthritis
Involves the production of autoantibodies against widely distributed antigens (nuclear components, DNA)
Autoimmune phenomena can also occur as a result of infections, malignancies, or immunodeficiencies
Molecular mimicry between pathogen and self-antigens can trigger cross-reactive immune responses
Autoinflammatory diseases, such as familial Mediterranean fever, involve innate immune dysregulation without autoantibodies or self-reactive T cells
Polyautoimmunity refers to the presence of multiple distinct autoimmune diseases in an individual
Causes and Risk Factors
Genetic predisposition plays a significant role in the development of autoimmunity, with multiple genes contributing to disease susceptibility
Human leukocyte antigen (HLA) genes are strongly associated with many autoimmune diseases
Environmental factors can trigger autoimmunity in genetically susceptible individuals
Infections, particularly viral infections, can initiate or exacerbate autoimmune responses through molecular mimicry or bystander activation
Toxins, drugs, and other chemical agents can modify self-antigens or alter immune regulation
Hormonal factors influence the development of autoimmunity, with many diseases being more prevalent in females
Estrogens can enhance humoral immunity and promote the survival of autoreactive cells
Immunological imbalances, such as defects in regulatory T cell function or overactive B cell responses, contribute to the loss of tolerance
Age is a risk factor, with many autoimmune diseases onset occurring in adulthood
Microbiome alterations and gut dysbiosis may disrupt immune homeostasis and promote autoimmunity
Autoimmune Diseases
Type 1 diabetes results from the autoimmune destruction of insulin-producing beta cells in the pancreas
Leads to insulin deficiency and hyperglycemia
Multiple sclerosis (MS) is characterized by autoimmune attacks on the myelin sheath of nerve fibers in the central nervous system
Causes neurological symptoms, including vision problems, muscle weakness, and coordination difficulties
Rheumatoid arthritis (RA) involves autoimmune inflammation of the synovial joints, leading to pain, swelling, and joint damage
Autoantibodies (rheumatoid factor, anti-citrullinated protein antibodies) are present in many cases
Systemic lupus erythematosus (SLE) is a systemic autoimmune disease affecting multiple organs, including the skin, joints, kidneys, and brain
Characterized by the production of autoantibodies against nuclear components (anti-nuclear antibodies)
Inflammatory bowel diseases (IBD), such as Crohn's disease and ulcerative colitis, involve autoimmune inflammation of the gastrointestinal tract
Psoriasis is an autoimmune skin disorder characterized by the formation of scaly, itchy patches
Autoimmune thyroid diseases, including Hashimoto's thyroiditis and Graves' disease, affect the function of the thyroid gland
Diagnosis and Testing
Autoantibody tests detect the presence of specific autoantibodies in the blood, aiding in the diagnosis of autoimmune diseases
Examples include anti-nuclear antibodies (ANA) in SLE, anti-citrullinated protein antibodies (ACPA) in RA, and anti-thyroid peroxidase (TPO) antibodies in Hashimoto's thyroiditis
Organ-specific functional tests assess the impact of autoimmunity on the affected organs
Glucose tolerance tests and insulin levels in type 1 diabetes
Thyroid function tests (TSH, T4) in autoimmune thyroid diseases
Imaging studies visualize the affected organs and detect inflammation or damage
Magnetic resonance imaging (MRI) in MS to detect brain and spinal cord lesions
Joint radiographs in RA to assess joint damage and erosions
Biopsy of affected tissues can reveal characteristic histological changes and confirm the diagnosis
Skin biopsy in psoriasis shows epidermal hyperplasia and inflammatory infiltrates
Genetic testing may identify predisposing genetic variants, particularly in familial cases or early-onset disease
Differential diagnosis is crucial to exclude other conditions with similar clinical presentations
Treatment Approaches
Immunosuppressive medications are used to dampen the overactive immune response in autoimmune diseases
Corticosteroids (prednisone) have broad immunosuppressive effects and are often used as initial therapy
Disease-modifying antirheumatic drugs (DMARDs), such as methotrexate and sulfasalazine, slow disease progression in RA and other conditions
Biologic therapies target specific components of the immune system involved in autoimmunity
Monoclonal antibodies against TNF-α (infliximab, adalimumab) are effective in RA, IBD, and psoriasis
B cell depletion therapy (rituximab) is used in RA and SLE
Organ-specific treatments address the consequences of autoimmune damage
Insulin replacement therapy in type 1 diabetes
Thyroid hormone replacement in Hashimoto's thyroiditis
Lifestyle modifications, such as diet and stress management, can help manage symptoms and improve overall well-being
Physical therapy and rehabilitation are important for maintaining function and preventing disability in conditions like MS and RA
Regular monitoring of disease activity and treatment response is essential to optimize outcomes and minimize side effects
Current Research and Future Directions
Identifying novel autoantibodies and biomarkers to improve the diagnosis and monitoring of autoimmune diseases
Development of antigen-specific assays for early detection and disease stratification
Investigating the role of the microbiome in the development and progression of autoimmunity
Exploring the potential of microbiome-targeted therapies (probiotics, fecal microbiota transplantation)
Developing antigen-specific immunotherapies to induce tolerance to specific self-antigens
Peptide immunotherapy in type 1 diabetes and MS
Chimeric antigen receptor (CAR) T cell therapy targeting autoreactive cells
Advancing personalized medicine approaches based on an individual's genetic and immunological profile
Pharmacogenomics to predict treatment response and optimize drug selection
Exploring the use of stem cell therapies to regenerate damaged tissues and organs
Autologous hematopoietic stem cell transplantation in severe autoimmune diseases
Investigating the role of epigenetic modifications in the development and progression of autoimmunity
Targeting epigenetic regulators (histone deacetylase inhibitors, DNA methylation modifiers) as potential therapies
Conducting large-scale, collaborative studies to unravel the complex interactions between genetic, environmental, and immunological factors in autoimmunity